Definitions:Topic 2 Flashcards
What is a cell membrane?
The selectively permeable membrane which surrounds the cytoplasm of a cell, acting as a barrier between the cell
contents and their surroundings
Define organelles.
sub-cellular bodies found in the cytoplasm of cells
What are enzymes?
Proteins that act as biological catalysts for a specific reaction or group of reactions
What are vesicles?
Membrane ‘bags’ that hold secretions made in cells
Define phospholipids.
Chemicals in which glycerol bonds with two fatty acids and an inorganic phosphate group
What are polar lipids?
Lipids with one end attached to a polar group (e.g. a phosphate group) so that one end of the molecule is hydrophilic and one end is hydrophobic
Define hydrophilic.
A substance with an affinity for water that will readily dissolve in or mix with water
Define hydrophobic.
A substance that tends to repel water and that will not mix with or dissolve in water
Define a monolayer.
A single closely packed layer of atoms or molecules
What are micelles?
A spherical aggregate of molecules in water with hydrophobic areas in the middle and hydrophilic areas outside
What is a bilayer?
A double layer of closely packed atoms or molecules
What is a unit membrane?
A lipoprotein membrane which is composed of two protein layers enclosing a less dense lipid
Define the fluid mosaic model.
The current model of the structure of the cell membrane including floating proteins forming pores, channels and
carrier systems in a lipid bilayer
What are gated channels?
Protein channels through the lipid bilayer of a membrane that are opened or closed, depending on conditions in the cell
What are glycoproteins?
Conjugated proteins with a carbohydrate prosthetic group
Define passive transport.
Transport that takes place as a result of concentration, pressure or electrochemical gradients and involves no energy from a cell
Define active transport.
The movement of substances into or out of the cell using ATP which is produced during cellular respiration
Define diffusion.
The movement of the particles in a liquid or gas down a concentration gradient from an area where they are at a relatively high concentration to an area where they are at a relatively low concentration
Define facilitated diffusion.
Diffusion that takes place through carrier proteins or protein channels
Define osmosis.
A specialised form of diffusion that involves the movement of solvent molecules down their water
potential gradient
Define partially permeable membrane.
A membrane which only allows specific substances to pass through it
What is a solute.
A substance in a solution, dissolved in the solvent
What is a carrier protein?
A protein that moves a substance through the membrane in active transport using energy from the breakdown of ATP or in passive transport such as facilitated diffusion down a concentration gradient
Define endocytosis.
The movement of large molecules into cells through vesicle formation
Define exocytosis.
The movement of large molecules out of cells by the fusing of a vesicle containing the molecules with the surface cell membrane; the process requires ATP
What is water potential?
A measure of the potential for water to move out of a solution by osmosis
What is osmotic concentration?
A measure of the concentration of the solutes in a solution that have an osmotic effect
What is an isotonic solution?
A solution in which the osmotic concentration of the solutes is the same as that in the cells
What is a hypotonic solution?
A solution in which the osmotic concentration of solutes is lower than that in the cell contents
What is a hypertonic solution?
A solution in which the osmotic concentration of solutes is higher than that in the cell contents
Define hydrostatic pressure.
The pressure exerted by a fluid in an equilibrium
Define turgor.
The state of a plant cell when the solute potential causing water to be moved into the cell by osmosis is balanced by the force of the cell wall pressing on the protoplasm
Define incipient plasmolysis.
The point at which so much water has moved out of the cell by osmosis that turgor is lost and the cell membrane begins to pull away from the cell wall as the protoplasm shrinks
Define plasmolysis.
The situation when a plant cell is placed in hypertonic solution when so much water leaves the cell by osmosis that the vacuole is reduced and the protoplasm is concentrated and shrinks away from the cell walls
What is ATPase?
An enzyme that catalyses the hydrolysis of ATP, releasing energy to move carrier systems and drive metabolic reactions
What is a cyanide?
A metabolic poison that stops mitochondria working
What is phagocytosis?
The active process when a cell engulfs something relatively large such as a bacterium and encloses it in a vesicle
What is pinocytosis?
The active process by which cells take in tiny amounts of extracellular fluid by tiny vesicles
What is a lung surfactant?
A special phospholipid that coats the alveoli and prevents them from collapsing
Define breathing (ventilation)?
The process in which physical movements of the chest change the pressure so that air is moved in or out
What is inhalation?
Breathing in
What is exhalation?
Breathing out
What are pathogens?
Microorganisms that cause disease
What is a catalyst?
A substance that speeds up a reaction without changing the substances produced or being changed itself
What are enzymes?
A proteins that act as biological catalysts for a specific reaction or group of reactions
Define specificity.
The characteristic of enzymes that means that each enzyme will catalyse only a specific reaction or group of reactions; this is due to the very specific shapes which come from the tertiary
and quaternary structures
What are anabolic reactions?
A reaction that builds up (synthesises) new molecules in a cell
What are catabolic reactions?
A reaction which breaks down substances within a cell
Define metabolism.
The sum of the anabolic and catabolic processes in a cell
Define a metabolic(metabolic pathway).
A series of linked reactions in the metabolism of a cell
What are intercellular enzymes?
Enzymes that catalyse reactions within the cell
What are extracellular enzymes?
Enzymes that catalyse reactions outside of the cell in which they were made
What is activation energy?
The energy needed for a chemical reaction to get started
What is a substrate?
The molecule or molecules on which an enzyme acts
Define the lock-and-key hypothesis.
A model that explains enzyme action by an active site in the protein structure that has a very specific shape; the enzyme and substrate slot together to form a complex in the same way as a
key fits in a lock
What is the active site?
The area of an enzyme that has a specific shape into which the substrate(s) of a reaction fit
Define induced-fit hypothesis.
modified version of the lock-and-key model of enzyme action where the active
site is considered to have a more flexible shape; after the substrate enters the active site, the shape of that site changes around it to form the active complex; after the products have left the complex, the enzyme returns to its inactive, relaxed form
Define molecule number(turnover number).
The number of substrate molecules transformed per minute by a single enzyme molecule
Define temperature coefficient(Q10).
The measure of the effect of
temperature on the rate of a reaction
What is denaturation?
The loss of the three-dimensional shape of a protein (e.g. caused by change in temperature or pH)
What is the initial rate of reaction?
The measure taken to compare the
rates of enzyme-controlled reactions under different conditions
What are mononucleotides?
Molecules with three parts- a 5-carbon pentose sugar; a nitrogen-containing base and a phosphate group - joined by condensation reactions
What is adenosine triphosphate (ATP)?
A molecule that acts as the universal energy supply. molecule in cells, inti
made up of the base adenine, the pentose supar ribose and three phosphate groups
Define deoxyribonucleic acid (DNA).
A nucieic acid that is the genetic material in many organisms
What is ribonucleic acid(RNA)?
A nucleic acid which is the genetic material in some organisms and is involved in protein synthesis
What is a ribose?
A pentose sugar that is part of the structure of RNA
What is deoxyribose?
A pentose sugar that is part of the structure of DNA
What is a purine base?
A base found in nucleotides that has two nitrogen-containing rings
What is a pyrimidine base?
A base found in nucleotides that has one nitrogen-containing ring
Define adenine.
A purine base found in DNA and RNA
Define guanine.
A purine base found in DNA and RNA
Define cytosine.
A pyrimidine base found in DNA and RNA
Define thymine.
A pyrimidine base found in DNA
Define uracil.
A pyrimidine base found in RNA
What are nucleic acids/polynucleotides?
Polymers made up of many nucleotide monomer units that carry all the information needed to form new cells
What is a phosphodiester bond?
Bond formed between the phosphate group of one nucleotide and the sugar of the next nucleotide in a condensation reaction
What are complementary base pairs?
Complementary purine and pyrimidine bases which align in a DNA helix, with hydrogen bonds holding them together (C-G,A-T)
What is a genome?
The entire genetic material of an organism
What is conservative replication?
A model of DNA replication which suggests that the original double helix remains intact and in some way instructs the formation of a new, identical double helix made up entirely of new material
What is semiconservative replication?
The accepted model of DNA replication in which the DNA ‘unzips’ and new nucleotides align along each strand;each new double helix contains one strand of the original DNA and one strand made up of new material
What are isotopes?
Different atoms of the same element, with the same number of protons but a different number of neutrons; isotopes have the same chemical properties
Define DNA helicase.
An enzyme involved in DNA replication that ‘unzips’ the two strands of the DNA molecules
Define DNA polymerase.
An enzyme involved in DNA replication that lines up the new nucleotides along the DNA template strands
Define DNA ligase.
An enzyme involved in DNA replication that catalyses the formation of phosphodiester bonds between the nucleotides
What is translation?
The process by which proteins are produced, via RNA, using the genetic code found in the DNA; it takes place in the ribosomes
What are ribosomes?
The site of protein synthesis in the cell
What is a triplet code?
The code of three bases that is the basis of the genetic information in the DNA
What is a gene?
A sequence of bases on a DNA molecule; it contains coding for a sequence of amino acids in a polypeptide chain that affects a characteristic in the phenotype of the organism
What is a codon?
A sequence of three bases in DNA or mRNA
Define messenger RNA(mRNA).
The RNA formed in the nucleus that carries the genetic code out into the cytoplasm
What is a complementary strand?
The strand of RNA formed that complements the DNA acting as the coding strand
What is the non-overlapping code?
A code where each codon codes for only one thing with no overlap between codons
What is a degenerate code?
A code containing more information than is needed
Define point mutation.
A change in a single base of the DNA code
What is a sense strand?
The DNA strand that carries the code for the protein to be produced
What is an antisense strand(template strand)?
The DNA strand which acts as a template for an mRNA molecule
What is a start codon?
The sequence of bases which indicates the start of an amino acid chain
What is RNA polymerase?
The enzyme that polymerises nucleotide units to form RNA in a sequence determined by the antisense strand of DNA
What is a stop codon?
One of three sequences of bases which indicate the end of an amino acid chain
Define transfer RNA(tRNA).
Small units of RNA that pick up specific amino acids from the cytoplasm and transport them to the surface of the
ribosome to align with the mRNA
Define the term anticodon.
A sequence of three bases on tRNA that are complementary to the bases in the mRNA codon
Define translation.
The process by which the DNA code is converted into a protein from the mRNA strand made in the nucleus
Define transcription.
The process by which the DNA sequence is used to make a strand of mRNA in the nucleus
What are polysomes?
Groups of ribosomes, joined by a thread of mRNA, that can produce large quantities of a particular protein
Define mutation.
A permanent change in the DNA of an organism
What are gametes?
Haploid sex cells that fuse to form a new diploid cell (zygote) in sexual reproduction
What is point mutation(gene mutation)?
A change in a single base of the DNA code
What is substitution?
A type of point mutation in which one base in a gene is substituted for another
What is deletion?
A type of point mutation in which a base is completely lost
What is insertion?
A type of point mutation in which an extra base is added into a gene, which may be a repeat or a different base
What are chromosomal mutations?
Changes in the position of entire genes within a chromosome
What are whole-chrosomal mutations?
The loss or duplication of a whole chromosome
Define variation.
Differences between organisms which may be the result of different genes or the environment they live in
What is a mutagen?
Anything that increases the rate of mutation
Define the term phenotype.
The physical traits, including biochemical
characteristics, expressed as a result of the interactions of the genotype with the environment
Define the term genotype?
The genetic make-up of an organism with respect to a particular feature
What are homologous pairs?
Matching pairs of chromosomes in an
individual which both carry the same genes, although they may have different alleles
Define the term locus.
The site of a gene on a chromosome
Define the term allele.
Versions of a gene, variants
Define homozygote.
An individual where both alleles coding for a particular characteristic are
identical
Define heterozygote.
An individual where the two alleles coding for a particular characteristic are
different
What does the term ‘dominant’ mean?
A characteristic which is expressed in the
phenotype whether the individual is homozygous or heterozygous for that allele
What does th term ‘recessive’ mean?
A characteristic which is only expressed when both alleles code for it; in other words, the individual is homozygous for the recessive trait
What is true breeding?
Homozygous organism which will always
produce the same offspring when crossed with another organism for the
same characteristic
Define monohybrid.
A genetic cross where only one gene for
one characteristic is considered codominance in heterozygotes, where both alleles at a gene locus are fully expressed in the phenotype
Define sex-linked traits.
Characteristics which are inherited on the sex chromosomes
What are autosomes?
Chromosomes which carry information about the body but do not determine the sex of an individual
Define homogametic.
An individual who produces gametes that contain only one type of sex chromosome - in humans this is the female
Define heterogametic.
An individual who produces two types of gamete each containing different types of sex chromosome - in humans this is the male
What are transcription factors?
Proteins that bind to the DNA in the nucleus and affect the process of converting or transcribing DNA into RNA
Define epigenetics.
The study of changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence but affects how cells read genes
Define sex-linked diseases.
Genetic diseases that result from a mutated gene carried on the sex chromosomes - in human beings, on the X chromosome red-green colour blindness, a sex-linked genetic condition which affects the ability to distinguish tones of red and green
Define haemophilia.
A sex-linked genetic disease in which one of the factors needed for blood to clot is not made in the body
What is cystic fibrosis(CF)?
A serious genetic disease caused by a recessive allele which affects the production of mucus by epithelial cells
What are exocrine glands?
Glands which produce substances and secrete them to where they are needed through a small tube called a duct
Define villi.
Finger-like projections of the lining of the duodenum and small intestine which increase the surface area for the absorption of digested food
What is the duodenum?
The first part of the gut after the stomach
What is the pancreatic duct?
The duct from the pancreas which carries digestive enzymes made in the pancreas into the duodenum
What is insulin?
Hormone made in the pancreas involved in the regulation of blood sugar levels
What is genetic screening?
When whole populations are tested for a genetic disease
What is phenylketonuria(PKU)?
A recessive genetic disorder where those affected lack the enzyme needed to digest the amino acid phenylalanine; the amino acid builds up in the blood and causes severe brain damage
What is prenatal screening?
Screening of an embryo or fetus before birth
What is amniocentesis?
A type of prenatal screening which involves removing a sample of amniotic fluid at around 16 weeks of pregnancy, culturing the fetal cells found and analysing them for genetic diseases
What is chrionic villus sampling?
A type of prenatal screening where a small sample of embryonic tissue is taken from the developing placenta and the cells tested for genetic diseases
What is preimplantation genetic diagnosis?
Testing the cells of an embryo produced by IVF to check for genetic diseases before it is implanted into the uterus of the mother
